New World monkeys (NWMs), also known as platyrrhines, live in tropical forest environments from southern Mexico down through South America. The name platyrrhine comes from the broad, flat, external nose characteristic of this group of primates. There are more than 50 species of NWMs, all of which are predominantly arboreal and herbivorous. NWMs are divided into two families: Atelidae and Cebidae.
The first family, Atelidae, is divided into three subfamilies: Atelinae, Callicebinae, and Pitheciinae. The four genera of Atelinae (howling monkeys, spider monkeys, woolly monkeys, and woolly spider monkeys) are the largest of the NWMs, each weighing approximately 10 kilograms. All members have long, grasping, prehensile tails that can be used as a fifth limb. The second subfamily, Callicebinae, has only one member, Callicebus (titi monkeys). Titi monkeys are monogamous and eat mostly fruits, but they also eat leaves and insects. The third subfamily, Pitheciinae, is composed of three genera: Cacajao, Chiropotes, and Pithecia. Pitheciines are known for their strong teeth and the ability to bite through the outer coverings of fruits and seeds that are generally too hard for other monkeys to open.
The second family, Cebidae, is composed of four subfamilies: Aotinae, Callithrichinae, Cebinae, and Incertae sedis. Like the Atelidae, some members of this family have prehensile tails. However, cebids have larger brains and more rounded, globular heads than do atelids. The first subfamily, Aotinae, has one genus, Aotus, commonly known as owl or night monkeys. Owl monkeys are the only nocturnal higher primate. As a result, they have the largest eye sockets of any anthropoid (higher primate). Individuals in the second subfamily, Callithrichinae, are the smallest NWMs. Callitrichines (tamarins, marmosets, and Goeldi’s monkeys) have derived claws (instead of nails) that enable them to cling to tree trunks while feeding. In the third subfamily, Cebinae, there are two genera: Cebus (capuchins) and Saimiri (squirrel monkeys). These two monkeys are the most omnivorous, as well as the most well-known, NWMs. In addition, there are at least a couple dozen NWMs that are extinct, many belonging to uncertain taxonomic positions grouped as I. sedis.
The evolutionary history of the NWMs extends back approximately 30 million years to the ancestral platyrrhines, who may have reached the New World by rafting across the Atlantic Ocean from Africa. One of the oldest platyrrhine fossils is the Oligocene primate Branisella.
Today, many NWMs are endangered, especially some of the callitrichines. Although some of the larger species are hunted, deforestation and popularity as pets generally pose the biggest threats to many NWM species. Woolly spider monkeys are one of the most critically endangered primates. Their numbers dropped from 400,000 when Europeans first arrived in South America to 700 in 1996. However, there is hope for some NWMs such as golden lion tamarins, which are a critically endangered species that, through captive breeding programs, have been reintroduced to the wild successfully and are slowly creeping back from the edge of extinction.
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